The present invention concerns a valve device for installation in pressurized gas or air piping and which may be controlled by means of the relative pressure of the gas applied to one port of the valve device or by the pressure differential between two ports thereof. That is, the state of the valve device may be remote-controlled via the air pressure in the pipe connected to that port, without auxiliary control lines, by varying the air pressure applied to the other end of the piping. In particular, it concerns a three-state valve device adapted to operatively adopt (i) a closed position, (ii) an open position between one pair of ports or (iii) an open position between another pair of ports, according to the pressure state in one of the ports, i.e. the valve control port.
The valve device of the present invention finds application for pumping (inflating) and unpumping (deflating) pressurized loads, in particular as a valve for a tire, such as a component for a tire-pressure control system in a motor-car vehicle. Such systems are used in transport vehicles, especially lorries and buses, since they enable corrective action to be carried out, either automatically or via driver manual control means, on the inflation state of each tire and/or wheel axle without having to stop, thereby providing an important safety feature for transport.
In the mentioned application, the valve device is inserted between one end of the piping of the installation and the air input of the tire, replacing or applying it to the conventional valve of the wheel and provides for the three fundamental operations of the system, that is: (i) to shut off the passage of air when the installation is underpressurized, to avoid the tires of the vehicle going flat, (ii) to enable sufficient air flow to pump a tire up or keep it inflated, in case of puncture for example, to avoid the vehicle having to stop anywhere, and (iii) to enable the tires to be deflated, for example for lowering the tire pressure because of road conditions.
In this application, the control port, which is coupled to one side of the plunger of the valve device, is connected to the piping. In addition to providing the state control pressure signal, at the same time it supplies the air (gas) for inflating; while a second port, coupled to the opposite side of the plunger, is connected to the tire tube and the third port may be arranged as a vent for airing pressure from the second port.
In the stated application, in addition to being able to pump the vehicle tires up, controllably and without stopping, it is also convenient to be able to deflate the tires, under control of a remote device, such as disclosed in Argentine patent application serial number P96.01.04874, published as AR004085 A1 on Sep. 30, 1998. To this end, a conventional 3-way valve, such as a solenoide for example, would not the best choice for the component identified by reference number 39 therein, to avoid having to lay out control lines to the position of the wheels which make the installation cumbersome apart from being difficult to protect against mechanical accidents.
This problem was initially overcome by means of the two-port valve device disclosed in Argentine patent application serial number P97.01.01607, published as AR006772 A1 on Sep. 29, 1999, which conventionally comprises a valve body having a passage extending therethrough between two air input/output orifices provided on opposite longitudinal ends of the valve body, a plunger housed in the passage and spring means for urging the plunger towards a valve seat in the passage for normally closing the passage, i.e., in absence of greater pressure in the piping of the installation. The valve is provided with means for graduating the degree of opening thereof that makes it selectively bidirectional, enabling it to adopt the following positions under control of the pressure in the piping:
closed (for example, when the installation is subjected to loss of pressure),
maximum degree of opening to pass air in the positive direction (inflating), when the input pressure or resultant force on the plunger is high enough to push the spring back, and
minimum degree of opening for air to return in the opposite direction (deflating). In this latter position of minimum degree of opening, the valve device enables a controlled amount of air to flow back through the piping of the installation.
Hence, one object of the invention is to provide a tire valve device useful as a component within an automatic vehicle tire pressure control system. Another object is a valve device that (i) remains closed in response to a depressurization of the system, regardless of whether the system has simply been shut off or because of mechanical failure in the piping of the installation, (ii) enables passage of air through the piping of the installation to pump the tire up, in order to recover or set a normal or desired pressure, and (iii) enables air to be vented to deflate the tire, without having to pass air back through the piping of the installation.
Another object of the invention is to be able to control the state of the valve device without external controls in the structure of the valve device but by means of the resultant pressure directly applied to the plunger on the basis of the state in the piping of the installation.
Yet another object is to pneumatically control the state of the valve device by means of the air pressure present at one side of the valve.
Yet a further object of the invention is a valve device of a simple yet sturdy construction, such that it is not too expensive considering the number of like devices a multi-axle vehicle needs and that the location (on the wheel) of installation of each, respectively, difficult to protect against strikes and jerks and, therefore, exposed to mechanical accidents, for example by stones picked up the same or another vehicle.
These and another objects and advantages brought out herein are achieved by means of a pressure-controlled three-way valve device comprising a valve body through which an inlet passage extends between an inlet port and a second port and houses a plunger coupled to elastic means urging it towards the inlet port. According to the invention, the valve body includes an outlet port preceded by an outlet valve having closed positions at respective opposite stroke limits of the plunger, such that it opens only in an intermediate position range of the plunger.
According to a preferred embodiment, the outlet valve comprises a pair of circumferential steps formed on the surface of the external wall of the plunger, between which there is an O-ring formed with two internal circumferential lips in register with the steps, such that, in both stroke limit positions of the plunger, a predetermined one of the steps abuts against a corresponding lip, closing the outlet port, which may open only through respective gaps formed between the seals and the corresponding seats in the intermediate position of the plunger. The inlet passage traverses the plunger longitudinally, passing through an inlet valve normally closed by a spring.
The above objects are essentially achieved because the plunger behaves, in fact, as a mobile seat for the inlet valve, providing an intermediate range of pressures where the longitudinal displacement of the plunger is used to control the outlet valve.
A method remotely controls the state of the valve device without additional control lines, to correct or maintain a desired pressure in the tire, varying the gas pressure in the piping connected to the inlet port. The method comprises: (i) to close the valve device, depressurize the piping; (ii) to open the inlet passage for pumping, pressurize the piping in a positive differential pressure range (i.e., greater than the air pressure in the tire); and (iii) to open the vent port and deflate the tire, apply air/gas to the inlet port at a pressure within a second range substantially lower than the pressure at the second port, that is a xe2x80x9cnegativexe2x80x9d differential relative to the second port (for example, initially depressurizing and then increasing the pressure at the inlet port to the desired pressure). In the first case, the valve device functions to protect the pressure present on the controlled side, whereas, in the other two cases, it functions to recover or correct the tire pressure under control, equalizing it to the pressure present in the piping.
In a more preferred embodiment, to improve reliability and operation speed of the valve device, the average initial friction of the O-ring is compensated by adding a second spring or equivalent elastic means to provide a threshold force urging of the plunger towards the inlet valve having a piston or closing means moveably seated on the plunger. This spring is in opposition to the first spring urging the inlet valve against the plunger and is dimensioned to yield to the force of the latter absent enough air pressure at the inlet port and, at the same time, urge the plunger to recover faster in response to a control pressure signal at the inlet port.
In an even more preferred embodiment, respective filters are arranged in both ports to protect the valve components from dust and dirt entering eventually via the ports and coming from the inflater system and the tire. These filters may be placed in these ports for seating the springs respectively urging the piston and the plunger.
The present invention may find application in medium and heavy road vehicles wherein the pump-up pressure of the tires is controlled via pressurized air piping connected to each controlled tire as a load of the piping by means of a respective valve device according to the invention.